The localization and mapping of mobile devices is a hot spot in the field of robot. There has been a practical solution to the self-localization of mobile devices in known environments and mapping with known locations of robots. However, in many environments the mobile device can't be localized by using global location system, moreover it is difficult or even impossible to obtain the map of the mobile device's working environment in advance. Hence the mobile device needs to build the map in a completely unknown environment under the condition that its position is uncertain, and use the map to locate and navigate autonomously. This is so-called simultaneous localization and mapping (SLAM).
According to the simultaneous localization and mapping (SLAM), the mobile device identifies characteristic indications in an unknown environment by utilizing sensors in the mobile device, and the global coordinates of the mobile device and the characteristic indications are estimated according to the relative position between the mobile device and the characteristic indication and the reading of the encoder.
So far, the most common exiting positioning techniques of automatic walking robots or devices are:                (1) GPS positioning; the basic principle of GPS positioning is based on instantaneous position of the satellite moving with high speed as a known starting data, and using the method of spatial distance resection to determine the location of the point to be measured.        (2) bar code positioning mode. To convert the bar code compiled according to certain rules into meaningful information, it is necessary to go through two processes of scanning and decoding. The color of the object is determined by the type of light it reflects, the white object can reflect the visible light of various wavelengths, the black object absorbs the visible light of various wavelengths, so when the light emitted by the bar code scanner light is reflected on the bar code, the reflected light is irradiated to the photoelectric converter within the bar code scanner, and the photoelectric converter converts reflected light signal into the corresponding electrical signal on the basis of different strength of the reflected light signal. According to difference principles, the scanner can be divided into three types: light pen, CCD and laser. After being output to the amplifying circuit enhancement signals of the bar-code scanner, the electric signals are transmitted to the shaping circuit to convert the analog signals into digital signals. The width of the black bars and black bars is different, hence the duration of the corresponding electrical signals is different. Then the decoder determines the number of bars and nulls by measuring the number of pulse digital electrical signals 0f 0 and 1. The width of the bar and the empty is determined by measuring the duration of the 0,1 signal. But the obtained data is still chaotic, in order to know the information contained in the bar code, it is necessary to convert the bar symbol into the corresponding number information and character information based on the corresponding coding rules (such as: EAN-8 yards). Finally, the details of the items will be identified through data processing and management by computer system.        
The positioning technique above applied in automatic walking robot or automatic walking equipment is relatively complex, each with different shortcomings:                1. GPS positioning is not practical due to signal problems in the room.        2. The bar code positioning mode is limited in usage occasions due to the fact that the bar codes are easily polluted and can not be read.        
Positioning and navigation technique of the mobile robot in the indoor environment has the characteristics of high precision and complicated environment for positioning, so the methods above are not applicable.